Conventional gas turbine engines include one or more rotors which are suitably mounted in bearings and supported by stationary frames. The frames provide rigidity for controlling the dynamic response of the rotor system and for minimizing blade tip clearances due to inherent flexibility during operation.
Multiple rotors in a gas turbine engine increase the complexity of the mounting system therefor, and engines having counterrotating power turbines yet further increase the complexity of the system. In one exemplary counterrotating power turbine design as disclosed in U.S. patent application Ser. No. 08/080,666, filed 6/18/93, entitled "Gas Turbine Engine Rotor Support System," assigned to the present assignee, a rotor support system includes rotating forward and aft turbine frames integrally joined to outer and inner rotors of a counterrotating power turbine. The turbine frames provide increased structural rigidity of the power turbine for controlling blade tip clearances, but since the turbine frames rotate, they are subject to centrifugally generated tensile stresses in the struts thereof. Accordingly, the struts must be suitably designed to accommodate the centrifugal tensile stresses for obtaining a suitable useful life of the power turbine.